Engineering materials experience damage during their lifetime, which reduces their ability to carry load and maintain structural integrity. Self-healing materials have been developed to mitigate the effects of damage, however, there are currently limitations in the healable length scale of damage that can be addressed. Overcoming this challenge requires a shift from simply re-bonding of cracks, which describes many current self-healing systems. Features of biological regeneration can be used to inspire approaches to address larger length scales of damage and achieve repeatable replacement of damaged or lost material. This thesis focuses on development of strategies for synthetic regeneration in polymers.
Concepts inspired by biological regeneration are applied to the problem of restoration of lost (damage) volume. Two specific damage modes that result in volumetric material loss are considered: impact puncture damage, and abrasive removal of a coating. This thesis focuses on demonstrating regeneration in response to these damage modes, and establishes experimental protocols for evaluation of performance. In addition, advancements are made in the fabrication of microvascular polymeric materials.
The transverse impact of plates of vascularized transparent polymer results in a multiscale damage pattern in which a centimeter-scale central puncture of lost (damage) volume is opened up where the projectile is incident, as well as a network of radiating microcracks emanating from the impact point. An embedded microvascular network facilitates the delivery of a novel two-stage healing agent to the site of damage in order to restore the lost damage volume. The performance of the restored specimens is evaluated by both seal testing under pressurization and impact energy absorption under repeat impact testing. Factors affecting the impact restoration performance are explored. The formulation of the two-stage healing agents is modulated to improve impact energy absorption. Sealing of 100% of samples is achieved by a hybrid system incorporating both a vascular network and microcapsules to separately target large damage (central puncture) and small microcracks.
Abrasive damage can result in complete removal of a protective coating and exposure of the underlying substrate. To regenerate the coating after damage, a single-part healing agent is released upon removal of the coating, and cures when exposed to simulated ambient sunlight. The regenerated coating is evaluated by hardness testing. Coating regeneration is facilitated by a pressurized microvascular system containing a compliant protective (UV blocking) valve. The polymeric coating is regenerated with the same hardness after large-scale removal, for four repetitive damage events (abrasion).
To improve control of the volume of healing agent released in response to damage, an accumulator is developed for incorporation into microvascular coating systems. The accumulator enables the localized storage of a prescribed volume of healing agent. Upon damage, this stored volume is released into the damage site. The accumulator is coupled with the UV blocking surface valve in a fully regenerative coating system. The volume control of the accumulator facilitates the regeneration of coatings with a consistent coating thickness over several repeat damage events.
Complex multidimensional microvascular polymers are created, enabled by sacrificial template materials spanning dimensionality from 0D to 3D. Templates are embedded in a thermosetting polymer and removed using a thermal treatment process called the Vaporization of Sacrificial Components (VaSC). The VaSC process results in a porous structure that is an inverse replica of the template. Vaporization of the template material is confirmed using both ex situ and in situ experimental methodologies, and the resulting vascular architectures are assesed by subjecting them to fluid flow experiments. Vascular architectures from each level of dimensionality (0D to 3D) are experimentally tested by applying fluidic pressure and measuring flow rate under laminar conditions. Experimental results are compared to appropriate predictive models (either analytical or computational fluid dynamics simulation) with good agreement. Thus, VaSCed architectures can be made accurately, with predictable flow characteristics. This work expands the range of microvascular architectures that can be fabricated in terms of size and geometry.